Methods for hydrogenating hydrocarbon resins to lighten the color are well known and generally produce a product that is "water white" in color. The aliphatic and/or aromatic unsaturation present in the resin is partially or completely eliminated, providing a product with improved oxidative stability, UV resistance and color stability. However, particularly in the case of resins derived from aromatic feedstreams, hydrogenation also alters the physical properties of the resin, which can make it less desirable for use in products such as adhesives, caulks and sealants, plastic and rubber modifiers, and printing inks. It would be advantageous to reduce the color of a resin without changing its other desirable physical characteristics.
Processes for improving the color of "hydrocarbon fractions" and hydrocarbon resins by selective hydrogenation of color bodies and color body precursors have been proposed. For example, U.S. Pat. Nos. 4,897,175 and 4,992,157 disclose a process for improving the color and color stability of "hydrocarbon fractions" such as kerosene, gasoline, straight run naphthas, diesel fuel and lubricating oils. The "hydrocarbon fractions" are contacted with hydrogen in the presence of a selective hydrogenation catalyst such as a Group VIII metal or a sulfided Group VIII metal, which may be on a porous support. Color bodies and color body precursors are hydrogenated.
U.S. Pat. No. 5,171,793 discloses the preparation of heat-stable, light colored resins by hydrogenation of resins produced by thermally polymerizing a feedstock containing a vinyl aromatic component, a cyclodiene component and optionally an acyclic diene component. The resin solution that results from the thermal polymerization is stripped to a softening point of 80.degree.-200.degree. C. before hydrogenation. The hydrogenation is carried out in the presence of (1) a hydrogenation catalyst selected from Group VIII metals, Group VI metals and Group VII metals, which may be activated or carried on a support; (2) a solvent diluent, and (3) an olefinic diluent. Chromophores and double bonds in the resin molecule are hydrogenated. U.S. Pat. No. 2,963,467 discloses a process for making light colored hydrocarbon resins with a softening point above 85.degree. C. by hydrogenating in the presence of a catalyst such as nickel, reduced nickel, nickel sulfide, copper chromite, copper molybdate, and molybdenum disulfide. However, the process also requires initial stripping of the polymerized resin to at least a 100.degree. C. softening point, followed by redissolving the resin in a diluent, and stripping the hydrogenated product at low temperatures and under reduced pressure.